This will be disconnected by the end of the week apperently
I think O2 classic 321 is on the 4G network. It will continue to work.
Recently found out, on the 321 you only need to make 1 call every 180 days to keep the sim active. There was a lot of misinformation online that said you needed to top up every 180 days.
O2 is even better value than RWG, which requires a call every 90 days.
Another tip: After a few years use, your punt sim will likely end up on client eye or have sergei trying to scam. The 321 and RWG are cheap plans that will likely dissapear. Just port a new number.
You can't port within the same network provider. (O2-O2 or RWG-RWG) Buy a 99p vodafone or EE sim and request the PAC. it's free to request the PAC.
If you're on O2, keep the little plastic card that contains the SSN number as it's needed to port a new number